1. Field of the Invention
This invention relates to the production of purified silicon suitable for use in solar cells. More specifically, the invention relates to the formation and separation of a silicon alkoxide and subsequent recovery of purified elemental silicon.
2. Description of the Prior Art
The production of solar grade (very high purity) silicon at a low cost is one of the prerequisites of an economically viable solar photovoltaic cell. At the present, a powdered metallurgical grade silicon of a purity of about 98.5% is available in large quantities on a commercial basis at what is considered a reasonable commodity price per pound. However, the level of concentration of impurities present in the silicon has to be reduced by a factor of 4 or 5 in order to even approach the desired purity for the solar voltaic cell applications. Unfortunately, the cost of the purification techniques is presently considered economically prohibitive.
Thus, over the last few years, there has been a growing interest in alternative methods for the preparation of low cost, high purity silicon. For example, chemical processes have been suggested such as the conversion of impure silicon tetrachloride to purify silicon by way of hydride formation and reduction/purification of silicon oxide by the reaction with carbon. Various ultra high temperature plasma reaction schemes have also been proposed such as the plasma zone refining of bars of silicon, purification of powdered silicon by successive acid leaching and plasma treatment and reduction/purification of silicon tetrachloride with sodium in a plasma reactor. However, all of these processes have experienced limited success either in terms of process expense and/or product purity.